Circulator



B. P. CHIRON Feb. 6, 1962 CIRCULATOR Filed Sept. 24, 1959 Fig,

2 1 H@9 1 fli fiilllllkd d M 3 m 7 HH M 1.

Fig

nited States Patent Gfice Patented Feb. 6, 1962 3,020,494 CHRCULATOR Bernard Pierre Chiron, Paris, France, assignor to Lignes Telegraphiqnes & Telephoniques, Paris, France Filed Sept. 24, 1959, Ser. No. 842,133 Claims priority, application France Jan. 19, 1959 4 Claims. (Cl. 3339) The present invention relates to a new four-port electrical network of the circulator type, in which ultrahigh frequency energy entering a first port is transmitted to a second port, but not to a third one, while the energy entering the second port is transmitted to said third port, but not to the first one, the fourth port being closed on a refiectionless termination impedance.

More specifically, the invention relates to a circulator using the directional properties of wave guides in which are inserted magnetic materials having gyromagnetic efiect when polarized by a steady magnetic field, such as ferrites or the like.

As is well known, such circulators are used, under the name of T.-R. switches in ultra-high frequency electromagnetic pulse transmitter-receivers for isolating the receiver from the transmitter during the sending of a pulse and, conversely, for isolating the transmitter from the receiver during time intervals in which pulses are received. Circulators have also been used in ultra-high frequency impedance measuring bridges and have recently been found very useful in connectionv with parametric amplifiers.

Known devices of the circulator type have also been built in the shape of waveguide lengths provided with magnetically polarized ferrite pieces so located therein as to give a propagating wave different phase shifts according to its transmission direction, these waveguide lengths being combined, for instance, with couplers of the magic'tee type. However, in such devices, a major part of the energy transmitted from an input port to an output port passes through the ferrite pieces. The latter, when submitted to too high an ultra-high frequency power, undergo excessive heating, which gives rise to. non-linear phenomena. Consequently, the power which can be transmitted through such a device is limited by the power the ferrite element is capable of handling without having its magnetic properties noticeably altered.

The present invention also makes use of the properties of certain magnetic material elements, such as ferrites which, by reason of the gyromagnetic effect they exhibit when polarized by a steady magnetic field, cause a wave propagating in a waveguide where they are located to undergo different phase shifts for its two possible propa gation directions. However, in the device of the invention, said elements are so arranged that they are submitted to a smaller fraction of the transmitted energy than it is the case in the previously known devices. Thus, with magnetic elements of comparable size, a significantly higher power can be handled by the circulator of the invention than by those of the previously known types.

One of the main features of the invention is the use of a pair of parallel and mutually coupled rectangular cross-section wave guides so arranged with respect to each other as to form four 8.34 decibels directional couplers, i.e. four such couplers in each one of which ultrahigh frequency energy transfer takes place (for instance through an aperture or aperture system of suitable shape and size provided in a common wall) from one guide to the other without the transmitted wave having its propagation direction changed but with an attenuation of substantially 8.34 decibels; i.e. a fraction substantially equal to or" the energy entering one guide is transmitted to the other. How such directional couplers may be built is explained, for instance, in a paper by S. E. Miller, entitled Coupled wave theory and waveguide applications and published in the review Bell System Technical Journal, vol. XXXIII, 1954, pp. 671-719. At page 694 of the same paper are given formulae al lowing to determine the value, the individual coupling factor of a number of successive identical directional couplers should have in order to cause total transfer of the energy entering one guide to the other guide. Numerical calculation using these formulae shows that, for the case of four couplers, the corresponding coupling factor must be precisely equal to or minus 8.34 decibels.

An important advantage of the system of the invention with respect to the devices of the previous art is that, in said system, each ferromagnetic material element is submitted to at most ,4 of the power entering the device, while, in the known devices, a more important fraction of said power passes through at least part of the ferromagnetic material elements.

Another characteristic feature of the system of the invention is that it includes a ferromagnetic material element and a dielectric material piece in each one of the two guides, and that said elements and pieces are set up in each one of said guides in such a way that they are separated, along the guide,'by two successive directional couplers, between which no dielectric or magnetic material is found.

In the hereinafter given description, it will be supposed, for simplicity, that the waves propagating in the waveguides are TE waves, but this should not be understood as a limitation of the scope of the invention.

According to the present invention, there is provided an ultra-high frequency four-port circulator, in which an input wave having a given frequency and a given propagation mode and applied to a first port is transmitted only to a second port, while an input wave of said given frequency applied to said second port is transmitted only to a third port, the fourth port being closed on a substantially reflectionless termination impedance, comprising first and second rectangular cross-section waveguide lengths having substantially identical cross-- from the next one by at least one-half of the phase' Wavelength in said guides for said mode and frequency, a first slab of low loss ferromagnetic material endowed with gyromagnetic effect when polarized by a steady magnetic field and set up in said first guide length between said first and second coupling means, a second slab of low loss ferromagnetic material endowed with gyromagnetic effect when polarized by a steady magnetic field and setup in said second guide length between said third and fourth coupling means, magnetic polarization means for impressing upon each one of said slabs a steady magnetic field substantially perpendicular to said guide axes, and first and second pieces of dielectric material set up in said first and second guide lengths respectively between said third and fourth coupling means and between said first and second coupling means; said four ports respectively consisting of each one of four openings, respectively constituted by one and the other of the ends of said first and second guide lengths.

According to a preferred embodiment of the invention, said coupling means between said guides consist of apere tures provided in a common wall to both said waveguides, said common wall being one of the narrower side walls of said guides.

According to the invention, said ferromagnetic slabs are so dimensioned that the differences between the phase shifts they introduce in the transmitted waves for one and the other of the two possible propagation directions in said guides are respectively equal to plus 180 degrees for one of said guides and to minus 18-3 degrees for the other guide, said propagation directions being re ferred to a common direction parallel to the axes of both guides.

Still according to the invention, said dielectric ma terial pieces are so dimensioned that they respectively introduce in the waves transmitted in the guides in which they are inserted, a phase shift substantially equal for one of said guides to the larger of the phase shifts introduced by the ferromagnetic element set up in the other guide for either propagation direction in the latter, and for this latter guide a phase shift substantially equal to the smaller of the phase shifts introduced for either propagation direction in said one of said guides.

In a known manner, phase shifts depending on propagation directions can be obtained by locating in the con sidered waveguide a slab of ferromagnetic material, such as ferrite, in a non-symmetrical position with respect to the symmetry plane of the waveguide parallel to its smaller side wall and by submitting said ferrite slab to a steady magnetic field perpendicular to that of the propagating wave and to its propagation direction. In such a condition, the apparent A.C. magnetic permeability of the ferromagnetic material is represented by an anti-symmetrical tensor and is consequently different according to which of the two possible propagation directions of the wave is considered.

The invention will now be described in greater detail with reference to the appended drawings, which show an embodiment of a circulator according to the invention, given as a non-limitative example thereof, and in which:

FIG. 1 shows a cross-section view of the circulator of the invention by a symmetry plane of the waveguides perpendicular to their narrower side walls.

FIG. 2 shows a cross-section view of this circulator by a plane perpendicular to the axes of the waveguides, together with magnets used in said circulator and shown in projection on said plane.

The circulator shown in FIG. 1 mainly consists of two parallel rectangular waveguides 1 and 2 with substantially identical cross-sections and having in common one of their narrower side walls and the ports" (i.e. openings) of which are designated by 3 and 4 for the first guide and by 5 and 6 for the second one, port 4 being closed by a suitable matched termination impedance, i.e. a reflectionless one. The two waveguides are mutually coupled by coupling means arranged so as to constitute four 8.34 decibel directional couplers 7, 8, 9 and 1t i.e. transmitting approximately f of the input energy applied to one of the guides to the other guide. These couplers may be built in any known manner.

In a preferred embodiment of the invention, each one of said directional couplers 7, 8, 9 and 10 is constituted by an aperture of suitable size and shape provided in a common wall to the two waveguides; the square root of the coupling factor of each one of these couplers, defined as the reciprocal of the ratio of the intensity of the electric field of the wave entering one of the guides before its passing through the aperture corresponding to that coupler to the intensity of the electric field of the wave in the other guide after its passing through said aperture, will be designated by sin (I, with a equal to 22 /2 degrees for a 8. 4 decibel coupler.

The distances between apertures pertaining to two successive couplers are not necessarily taken equal, but each one of them must be chosen at least equal to half the phase wavelength in the guide for the propagation mode and frequency of the transmitted waves.

A piece of dielectric material 11 is set up in guide 1 between couplers 7 and 8, while in guide 2 a ferrite slab 12 is set up between the same couplers. In a similar way, in waveguide 1, a ferrite slab 13 is set up between couplers 9 and 10, while in waveguide 2 a piece of dielectric material 14 is set up between the latter said couplers 9 and 10. Each ferrite slab is located in a nonsymmetrical position with respect to the symmetry plane of the guide parallel to the common wall to both waveguides. Each ferrite slab is submitted to a transversal steady magnetic field perpendicular to the broader side walls of the waveguide (the width of which is designated by n in FIG. 1), which gives different phase shifts to waves propagating in opposite directions in the same guide, The dimensions of the ferrite slabs are respectively chosen in such a manner that the part of the waveguide in which the ferrite slab 13 is located causes a phase shift 1) higher than 180 degrees for the wave propagating from left to right in guide 1 (FIG. 1) and a phase shift (b-c), where c is substantially equal to degrees, for the waves propagating in the reverse direction in the same guide. In the other guide 2, the dielectric material piece 14 causes equal phase shifts for both propagation directions. Thanks to a suitable choice of the dimensions of 14, these phase shifts are given a common value equal to b. In the same way, in waveguide 2, the ferrite slab 12 causes a phase shift d for the wave propagating from left to right and a phase shift (d-l-c) for the wave propagating in the reverse direction with c substantially equal to degrees. The part of the guide 1 where the dielectric material piece 11 is located causes equal phase shifts of value d for both propagation directions, thanks to a suitable choice of the dimensions of 11.

The parts of both guides located between couplers 3 and 9 do not contain any ferrite slab or dielectric material piece. As it has been mentioned above, with regard to the distances between any two successive couplers, its length m must be at least equal to half the phase wavelength in each guide for the frequency and propagation mode of the transmitted waves.

The planes perpendicular to the longitudinal axes of the guides and corresponding to the left and right ends of the various directional couplers in FIG. 1 will be designated hereinafter by 15-16, 17-18, 19-20, 21-22, 23-24, 25-26, 27-28 and 29-30.

The steady magnetic fields applied to ferrite slabs 12 and 13 are respectively obtained from permanent magnets 31 and 32, of which, in FIG. 1, only the cross-section by the plane of said figure is shown.

FIG. 2 is a cross-section view of the device of FIG. 1 by plane 17-18, except for magnets 31, 32 and ferrite slabs 12 and 13 of FIG. 1 which are shown in projection on said plane. FIG. 2 shows a possible arrangement of the positions of these magnets with respect to the ferrite slabs they magnetically polarize and to the cross-sechons of the guides. This arrangement ensures that the abovementioncd relationship be obtained between the various phase shifts introduced by slabs 12 and 13 in the waveguides in which they are respectively located, for each one of the two possible propagation directions in said guides.

Referring now again to FIG. 1, the operation of the device of the invention may be briefiy explained as follows:

The ultra-high frequency energy which enters guide 1 through port 3, after its crossing the coupling aperture 7, partly propagates into part 18-20 of guide 2, while its remaining part propagates into part 1719 of guide 1. If the high frequency electric field at the input of guide 1 has an amplitude E, the corresponding field amplitude at the input of part 18-29 of guide 2 is, in comple ycctor notation, equal to sin a) (with j equal to /-l) and that at the input of part 17-19 of guide 1 is equal to E cos a.

After undergoing phase shifting in these parts of the guide, the energy transmitted by each part of the split wave enters the second directional coupler corresponding to aperture 8. At the input 21 of part 21-23 of guide I enters a wave constituted by part of the wave coming from 19 and part of the wave coming from 20; the same is true of the wave at the input 22 of part 22-24- of guide 33 2, and the same energy division process continues up to the end ports 4 and 6 of the device.

The ultra-high frequency energy from the transmitter applied to port 3 of guide 1 is divided in the directional coupler 7 into two parts, each of which propagates in one of the guides toward the next directional coupler, and so on till the far end of the device is reached. The dividing of the energy takes place according to a rule given by S. E. Miller in the cited paper. The ratios of the ampli tudes, at the outputs of a directional couplerin first and second guides, to the electric field amplitude in the first guide at the coupler input are respectively equal to cos. a and j sin. a (where j equals 1) Taking further in account the phase shifts in the parts of the guides comprised between two successive directional couplers, the relative electric field amplitudes in either guide at the input to a directional coupler and just beyond it, referred to the amplitude E of the electric field at port 3 of guide 1, are given in the following table:

Ratio of electric field amplitude at points numbered in FIG. 1 to input electric field amplitude ej sin a 21 and 23 ecos a+e- (j sin a) =ecos 2a 22 and 24...- ecos aj sin a+ej sin a cos a=jesin 2a 2 2- cos 21: cos a+je-i sin 2a j sin a=ecos 3a It can be seen that on one hand the ratio of the respective intensities of the electric fields at port 6 and 3 is equal to e sin 4a, and that on the other hand the ratio of the respective field intensities at ports 4 and 3 is equal to r cos 4a. As a is taken equal to 22%. degrees, the modulus of the first ratio is equal to one and the modulus of the second is zero. The whole energy is consequently transmitted from port 3 to port 6, none being received at port 4.

The ratio of the field intensity at 18 to that at 15, which is the field intensity E at the input of guide 1, is equal to (-i sin a) and that of the field at 23 to E is equal to r cos 3a or r sin a (since a equals 22 /2 degrees). The modulus of both of these ratios is thus equal to (sin a), with at equal to 22 /2 degrees. it results therefrom that the ratio of the power applied to each one of the two ferrite slabs to the input power of the device is equal to sin a, i.e., -If, for instance, the peak input power is one megawatt, the peak power applied to each ferrite slab is only 145 kilowatts.

A similar calculation would show that, since c is given a value equal to 180 degrees, the whole of the power of a wave entering guide 2 through port 6 would be transmitted to port 5, no power being transmitted to port 3. This results from the fact that, although in the latter case the ferrite slabs 12 and 13 play a part much similar to that played in the former case, except for their reverse order, the difference in the individual dimensioning of the dielectric pieces 11 and 14, together with their reverse operating order, results in a relative phase reversal of the waves combining at each one of couplers 9 and 7, and consequently in the total transfer of the energy to port 5 instead of port 3.

Although, in the hereinabove given description, the operation of the system of the invention has been explained as that of a three-port device, it must be understood that any one of ports 3, 4, 5 and 6 of FIG. 1 could be closed on a refiectionless termination, the three remaining ports then being the useful ones. This justifies the description of the system as a four-port device.

What is claimed is:

l. A four-port circulator for the transmission of an ultra-high frequency wave having a given frequency and propagation mode, comprising first and second rectangular cross-section waveguide lengths having substantially identical cross-sections and parallel longitudinal axes, first, second, third and fourth coupling means successively distributed along both said guide lengths and constituting four 8.34 decibels directional couplers, each one of which is spaced from the next one by at least one-half of the phase wavelength in said guides for said mode and frequency, a first slab of low loss ferromagnetic material endowed with gyromagnetic effect when polarized by a steady magnetic field and set up in said first guide length between said first and second coupling means, a second slab of low loss ferromagnetic material endowed with gyromagnetic effect when polarized by a steady magnetic field and set up in said second guide length between said third and fourth coupling means, magnetic polarization means for impressing upon each one of said slabs a steady magnetic field substantially perpendicular to said guide axes, and first and second pieces of dielectric material set up in said first and second guide lengths respectively between said third and fourth coupling means and between said first an second coupling means; said four ports respectively consisting of each one of four openings respectively constituted by one and the other of the ends of said first and second guide lengths; wherein said ferromagnetic slabs are so dimensioned that the differences between the phase shifts they introduce in the transmitted waves for one and the other of the two possible propagation directions in said guides are respectively equal to plus degrees for one of said guides and to minus 180 degrees for the other guide, said propagation directions being referred to a common direction parallel to the axes of both guides; wherein said dielectric material pieces are so dimensioned that they respectively introduce in the waves transmitted in the guides in which they are inserted a phase shift substantially equal for one of said guides to the larger of the phase shifts introduced by the ferromagnetic element set up in the other guide for either propagation direction in the latter, and for this latter guide a phase shift substantially equal to the smaller of the phase shifts introduced for either propagation direction in said one of said guides; wherein one of said four ports is closed on a refiectionless termination impedance; and wherein each one of said ferromagnetic material slabs is located in one of said guides in a position closer to one of the narrower side walls of said one of said guides than to the other of said narrower side walls.

2. A circulator as claimed in claim 1, wherein said ferromagnetic material slabs are made of a low loss ferrite.

3. A circulator as claimed in claim 1, wherein said coupling means between said guides consist of apertures provided in a common wall to both said waveguides, said common wall being one of the narrower side Walls of said guides.

4. A circulator as claimed in claim 1', wherein said magnetic polarization means consist of a pair of permanent magnets.

References Cited in the file of this patent UNITED STATES PATENTS 2,849,685 Weiss Aug. 26, 1958 FOREIGN PATENTS 1,162,276 France Apr. 8, 1958 

